1. Field of the Invention
The present invention relates to the substitutes wax with plastic sleeving plastic sleeving to form dental coping and pontic substructures which act as the support system for several overlays of dental acrylics or porcelains in fabricating a completed dental restoration. A completed restoration is the result of a series of process: first, the plastic; second, the investment to metal; and third, the acrylic or porcelain overlay. Step one, the plastic stage and step two, the "metal stage", will be the focus of this invention.
2. Description of the Prior Art
Forming the coping and pontic structure is a necessary step in the fabrication of dental crowns and bridges. A single tooth that has been clinically prepared by the dentist supports a single coping. A pontic spans between two copings to form a bridge. One or more crowns are constructed upon and supported by a pontic or pontics to replace a tooth or teeth where none exist.
Conventionally, the wax coping and pontic are transformed from wax to metal through the "lost wax" process in which the coping and the pontic are modeled by hand of wax by dipping, flowing, building, layering and hand carving to a precise design and thickness. The wax is sprued, invested, burned out in a high-heat oven and cast in metal in a centrifuge using high fusing alloys. To form a crown for restoring the dentition, the metal coping and pontic is usually covered with a color coating of an acrylic or fired-on porcelain ceramic composition for the purpose of aesthetics as well as function. The metal coping (or pontic) supports the coatings and provides the required structural strength and rigidity for the restored tooth or teeth to resist the force of mastication. The ultimate goal of the conventional wax-to-metal process is to create metal copings and pontics that exactly fit the original clinical preparation. Distortion, expansion, shrinkage, microcracks and impurities are undesirable. Because wax remains unstable, the use of wax causes many of these problems. As evidenced by recent patents, attempts have been made to alter the wax-to-metal process and to even eliminate the lost wax process. Because the materials and processes described in these patents are excessively costly, time consuming and/or non-flexible in design, they have not been accepted in the dental industry as practical alternatives to using wax.
Several methods have been proposed that use metal foil as an alternate to the wax and the lost wax casting method. U.S. Pat. Nos. 4,838,790, 4,861,267 and 490,637 disclose methods of forming a sleeve in which a thin sheet of metal foil is configured to the die. Typically, this sleeve is fused by heating. The metal foil methods have one or more drawbacks. They are time consuming; they are not easily adaptable to all size and shape dies; the results are highly operator dependent; and overlapping metal folds yield variable wall thickness and stress-riser ridges which affect the acrylic or porcelain overlays.
Therefore, the intent of this invention is to introduce a new medium, known as shrink plastic sleeving, for producing copings and pontics intermediate plastic substructures that overcome the shortcomings of the prior art.
It is desirable that the improved coping and pontic intermediate plastic substruct include openings for providing additional gripping attachment of the crown.
Also it is desirable that the improved coping or pontic intermediate plastic substructure include openings to minimize the volume of the coping or pontic intermediate plastic so as to reduce the amount of precious metal used and to increase the amount of acrylic or porcelain overlay material in the perforated areas which aids in aesthetics.
It is also desirable that the volume of the improved coping and pontic intermediate plastic substucture be reduced so as to minimize weight as well as the amount of precious metal used.